P1166

DTC P1166: HO2S Circuit Low Voltage During Power Enrichment Sensor 1

System Description
The internal circuitry of the Engine Control Module (ECM) can identify if the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration (power enrichment). When a Power Enrichment (PE) mode of operation is requested by heavy acceleration during Closed Loop operation, the ECM will provide more fuel to the engine. Under these conditions the ECM should detect a rich condition. If this rich condition is nor detected at this time, Diagnostic Trouble Code (DTC) P1166 will set. A restricted fuel line can prevent adequate amount of fuel from being supplied during Power Enrichment mode.

Conditions for Setting the DTC
- HO2S1 voltage is less than 0.35 V in Power Enrichment (PE) mode.
- Engine is operating in Closed Loop and in PE mode.
- Engine Coolant Temperature (ECT) is greater than 60 °C (140 °F).
- System voltage is greater than 10 V.
- Air/Fuel ration is less than or equal to 13.5 : 1.
- Airflow is greater than 6 g/s.
- 2 second delay after in PE mode.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.
- The vehicle will operate in Open Loop.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after four consecutive ignition cycle in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- The DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds.

Diagnostic Aids
Water or alcohol fuel may cause low HO2S1 voltage during acceleration.

Check for adequate amount of fuel in the Tank.

When the engine is idling or at steady cruise, the HO2S1 voltage should vary from between approximately 100 - 900 mV. During power enrichment mode, more fuel is needed, and the HO2S1 should rise above 444 mV.

Check for faulty or plugged injector(s).

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred.
The information is then stored on the scan tool for later reference.
2. This step checks to see if the HO2S1 is operating properly.
3. If no faults have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information. Diagnostic Aids

Step 1-6:

Troubleshooting